At approximately 11:55 p.m. (UTC-8), CHP officers Walt Frago and Roger Gore conducted a traffic stop of Bobby Davis and Jack Twining in conjunction with an incident involving the pair that had been reported to the CHP minutes earlier. After stopping in a restaurant parking lot and initially cooperating with the officers, Twinning and Davis opened fire and killed both officers. Minutes later, Officers George Alleyn and James Pence arrived on the scene and engaged Twinning and Davis in a shootout. A passerby picked up one of the officers' weapons and opened fire on the perpetrators; however, the three were outgunned, and both Alleyn and Pence suffered fatal injuries while the passerby ran out of ammunition and took cover in a ditch. A third CHP patrol car arrived on the scene and the lone officer inside briefly exchanged gunfire with the perpetrators, but they were able to flee the scene.

Over three hours later, after stealing a vehicle and exchanging gunfire with its owner, Davis attempted to flee the area; however, he was spotted by police and arrested. Meanwhile, Twinning broke into a house and took one of its occupants hostage. The house was surrounded by deputies of the Los Angeles County Sheriff's Department and at approximately 9 a.m., he released the hostage and committed suicide when the deputies entered the house. Davis was sentenced to death but had his sentence commuted to life imprisonment without the possibility of parole in 1973. He killed himself[3] at Kern Valley State Prison in 2009.[1]

The Newhall incident resulted in a number of changes at the CHP, including procedural changes in arresting high risk suspects and standardization of firearms and firearms training used across the department.[1][2]

Jack Twinning, age 35, and Bobby Davis, 27, were both career criminals with long histories of violent felonies. Twinning had been in and out of eight different federal prisons since age 16, including a 5-year stint at Alcatraz in which he killed another prisoner in self-defense. He had been released from a federal prison in Tallahassee, Florida 11 months prior to the shootings. Davis had been released from prison 8 months prior to the shootings and was on parole in Houston, Texas. Twinning and Davis met and became friends in prison.[4]

After failing to land jobs following their release from prison, Twinning and Davis met up again in Houston, and drove to Sacramento, California, where they failed in their attempt to rob banks. They then drove down to Los Angeles in a red 1964 Pontiac.[4] En route to Los Angeles, they noticed construction along the highway in the mountainous area near Gorman and believed they could steal explosives from that site in order to commit a robbery.[5]

Twinning and Davis rented an apartment in Long Beach. Soon after, they began observing an armored car delivering cash to Santa Anita Park. They devised a scheme to use explosives in order to rob it on a freeway offramp,[4] and returned to the construction site to procure the explosives. Inside their red Pontiac, they had amassed numerous weapons, including handguns, rifles, and shotguns. Overall, they had twice as many weapons as the four CHP officers they would eventually face had in their two patrol cars.[5]

On the evening of April 5, Davis dropped Twinning off in the mountains to steal the explosives. At approximately 11:20 p.m. (UTC-8), Davis was driving northbound on Interstate 5 south of Gorman when he made an illegal U-turn across the highway median, nearly colliding with a southbound vehicle being driven by Ivory Jack Tidwell, a military serviceman en route to Port Hueneme with his wife in the passenger seat.[6] Tidwell had a verbal argument with Davis and both stopped their vehicles, where Davis brandished a firearm. Tidwell managed to convince Davis the CHP was in the area, which prompted Davis to drive away. The couple immediately drove to a phone and reported the incident complete with a description of Davis' vehicle to the CHP.[5] Officers in the area were informed the vehicle was wanted in connection with a misdemeanor, as the area – now a sprawling suburban area – was sparsely populated at the time, and hunting and shooting were allowed.[4][6]

Several minutes later, CHP officers Walt Frago and Roger Gore, partners in the same patrol car, spotted the red Pontiac near Castaic and began following the vehicle. Officers James Pence and George Alleyn, partners in a second patrol car, waited in nearby Valencia ready to back up Frago and Gore. The suspect vehicle exited the freeway at Henry Mayo Drive, near the present-day site of Six Flags Magic Mountain, and pulled into a restaurant parking lot. Frago and Gore ordered the two occupants to exit their vehicle. Obeying the officer's orders, Davis exited the driver's seat and walked to the front hood of the vehicle where Gore proceeded to search him. Meanwhile, Frago approached the other side of the car carrying a shotgun at "port arms" with the stock against his hip and the barrel pointed in the air.[4][6]

As Frago walked to the Pontiac, Twinning exited the passenger seat and opened fire with a Smith & Wesson Model 28 revolver. Before Frago could aim or fire his shotgun at Twinning, he was struck by two .357 Magnum rounds and killed. Gore immediately drew his service pistol and returned fire at Twinning, but in doing so lost track of Davis, who was right next to him. While Twinning and Gore exchanged gunfire, Davis pulled a .38 Special caliber Smith & Wesson Model 49 revolver out of his waistband and killed Gore with two shots at point blank range.[6]

Shortly after Gore was killed, Alleyn and Pence arrived on the scene. Davis and Twinning immediately opened fire on them with their pistols, expending all their remaining rounds, and then dove back into their own car for new weapons. Davis pulled out a sawed-off shotgun, while Twinning grabbed a semi-automatic Colt M1911.45 ACP caliber pistol. After firing one shot, Twinning's 1911 jammed, but he simply grabbed another one from the car and exited the driver's side. Meanwhile, Alleyn emptied his Remington Model 870 shotgun at the Pontiac, firing the gun so fast he accidentally ejected a live round in the process. A single pellet from the shotgun struck Twinning in the forehead, but it did not penetrate his skull and only inflicted a minor superficial wound. After expending all his shotgun rounds, Alleyn opened fire on Davis with his .357 Magnum revolver, but did not make any hits. Davis returned fire with his sawed-off shotgun, striking Alleyn with several rounds of 00 buckshot and inflicting fatal injuries.[4][6]

Gary Kness, 31, a former U.S. Marine, was en route to work when he came upon the shootout. Kness got out of his vehicle and ran over to the fallen officer Alleyn. He tried to drag Alleyn to safety, but was unable to move him. He looked up and saw Davis discard his now-empty sawed-off shotgun and grab the Remington shotgun that had been dropped by Frago. Without realizing Frago had never fired the gun, Davis tried to cycle the action of the shotgun, but since it had not been fired, it was locked on a live round. Eventually, he accidentally fired the gun into the air. Startled, he dropped the weapon and grabbed the service pistol from Frago's holster.[7]

Meanwhile, on the other side of the cruiser, Pence fired all six rounds from his .357 Magnum revolver at Twinning but missed. Twinning returned fire with his Colt 1911, hitting Pence in the chest and in both legs. Pence fell to the ground, trying to reload. At the time, the CHP did not issue speedloaders to their officers, forcing Pence to manually reload one round at a time. On the other side of the cruiser, Kness picked up Alleyn's discarded shotgun and tried to fire at Davis, but the gun was empty. As Davis opened fire on him with Frago's pistol, Kness dropped the shotgun and returned fire with Alleyn's service revolver. His shots hit the Pontiac, and a fragment from one of the bullets lodged into Davis' chest but the shot did not incapacitate Davis, and Kness was soon out of ammunition.[7]

While this was going on, the wounded Pence was still attempting to reload his revolver. As he did so, he failed to notice Twinning sneak up to the cruiser and around the left side. As he inserted the sixth cartridge and started to close the cylinder of his weapon, behind him, Twinning killed Pence with two shots to the head at point blank range. Realizing his situation was now hopeless, Kness ran from the cars to cover in a nearby ditch. As he did, a third CHP cruiser arrived at the scene. After a brief exchange of gunfire with the lone officer, the two suspects fled the scene through the darkness in separate directions. Davis took Frago's revolver with him, while Twinning ran off with Pence's revolver and Frago's shotgun.[7]

At 3:25 a.m. Davis stumbled onto a camper parked near a dirt road. After exchanging gunfire with the owner, Daniel Schwartz, armed with a World War II surplus Enfield revolver, Davis pistol-whipped Schwartz with his empty revolver and stole the camper. Schwartz called the police and reported the theft. Within hours the camper was spotted and pulled over by deputies from the Los Angeles County Sheriff's Department. Without any more loaded guns at his disposal, Davis surrendered.[5]

Three miles away from the scene of the shootout, Twinning broke into a house and took one of the occupants hostage. The occupant's wife and son managed to escape and called police, and soon the house was surrounded by officers from the Los Angeles County Sheriff's Department. For the next several hours, negotiators talked on the phone with Twinning, who openly bragged about how he took advantage of Frago's mistake when he saw the officer approach his car with the shotgun in an un-shootable position: "He got careless, so I wasted him."[8] By roughly 9 a.m., Twinning released his hostage from the house. After issuing a surrender ultimatum, police pumped tear gas into the house and stormed in. As police entered the residence, Twinning committed suicide with Frago's shotgun.[6][7]

Davis was sentenced to death for the murders of the four CHP officers. However, in 1972, Davis' sentence was commuted to life in prison without parole, due to the U.S. Supreme Court ruling in Furman v. Georgia that invalidated all death sentences in the nation. Davis was found dead, aged 67, in his maximum-security single cell at Kern Valley State Prison, an apparent suicide, on August 16, 2009.[9]

After the shootout, the circumstances of the event were scrutinized, causing the CHP and other police departments to re-examine their methods of training and tactics.[1]

None of the four CHP officers who were killed had more than two years of experience on the job. Gore and Frago were both 23 years old, while Pence and Alleyn were both 24. None were wearing bulletproof vests, which were not commonly issued to police officers at the time. Three of the policemen died from wounds that a standard ballistic vest might have prevented.[10] A key mistake made by Gore and Frago was proceeding to approach and search the suspects immediately after pulling over. Had they waited for Pence and Alleyn to arrive within a minute or so, it is possible Twinning and Davis would have surrendered or been overwhelmed by superior firepower when faced with 4-on-2 odds.[11]

The three officers who fired their handguns were using .357 Magnum rounds, although they had only been trained and certified with .38 Special ammunition, which has less recoil. Soon after the shootout, the CHP standardized their ammunition on the .38 caliber round, ensuring all officers trained with the same ammunition they would use on duty. Lack of familiarity with their service shotguns was also cited as a problem during the shootout, as evidenced by Frago's mistake of approaching with his shotgun held diagonally in front of his body and Alleyn's error of ejecting a live round.[7]

An issue brought up by the Newhall incident was the difficulty in reloading revolvers under fire without a speedloader, something that may have cost Pence his life. Shortly afterward, the CHP became the first major state police department to approve and issue speedloaders. A backup gun might have aided Pence when his primary revolver ran dry.[12]

While there were a number of lessons learned in the aftermath of the Newhall incident, a rumor that Officer Pence took the time to put his spent brass cases in his pocket while reloading during the shooting, because of a habit developed on the police shooting range, was determined to be untrue. The rumor arose soon after the shooting, during the time that the CHP made improvements to their training. While the CHP did modify their training to eliminate the practice of "pocketing brass" on the range in the aftermath of the Newhall shooting, this was not based on the actions of any officer involved in the incident. A number of witnesses, including officers who responded to aid the four officers, made it clear that no brass was found in Officer Pence's pants or jacket pockets. CHP Sergeant Harry Ingold (retired) was one of the first cover officers to arrive on the scene the night of the shooting. Ingold found six brass cases on the ground next to the driver's door of Pence's and Allyn's cruiser. Prior to being murdered, Pence had dumped his brass on the ground before partially reloading his revolver. This information has been confirmed by Chief John Anderson, author of The Newhall Incident: America's Worst Cop Massacre.[14]